Ginzton Lab

The vast majority of the greatest scientific discoveries of all time have resulted directly from more powerful techniques for measuring light. Indeed, our most important source of information about our universe is light, and our ability to extract information from it is limited only by our ability to measure it.

Interestingly, most of the light in our universe remains immeasurable, involving long pulses of relatively broadband light, necessarily involving ultrafast and extremely complex temporal variations in their intensity and phase. As a result, it is important to develop techniques for measuring, ever more completely, light with ever more complex submicron detail in space and ever more complex ultrafast variations in time. The problem is severely complicated by the fact that the timescales involved correspond to the shortest events ever created, and measuring an event in time seems to require a shorter one, which, by definition, doesn't exist!
Nevertheless, we have developed simple, elegant techniques for completely measuring such light, using the light to measure itself and yielding a light pulse's intensity and phase vs. time and space. One technique involves making an optical spectrogram of the pulse using a nonlinear optical medium and whose mathematics is equivalent to the two-dimensional phase-retrieval problem—a problem that's solvable only because the Fundamental Theorem of Algebra fails for polynomials of two variables. In addition, we have recently developed simple methods for measuring the complete spatio-temporal electric field [E(x,y,z,t)] of an arbitrary, potentially complex light pulse without the need to average over multiple pulses.

Metamaterials have attracted tremendous attention due to their exotic optical properties and functionalities that are not attainable from naturally occurring materials. In particular, metamaterials can be designed to introduce strong spin-orbit coupling for light and consequently nontrivial topological properties. In this talk, I will start with a brief introduction to the concepts of Berry curvature, Chern number and topological photonics. I will show that combination of chirality and hyperbolicity – an extreme form of anisotropy, can result in nontrivial topological orders in metamaterials and consequently topologically protected photonic surface states that are immune from scattering by defects and sharp edges. The Weyl points in such systems result from the crossing between the bulk longitudinal plasmon mode and the transverse circularly polarized propagating modes. The photonic 'Fermi arcs' were directly observed in the microwave regime, which showed Riemann-surface like helicoid configuration in the energy-momentum space. I will further show that by designing the Weyl metamaterials with inhomogeneous unit cells, artificial magnetic field can be introduced which leads to the first observation of chiral zero Landau mode in photonic systems.

AP 483 & AMO Seminar Series
Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

The turbid nature of refractive index distribution within living tissues introduces severe aberrations to light propagation thereby severely compromising image reconstruction using currently available non-invasive techniques. Numerous approaches of endoscopy, based mainly on fibre bundles or GRIN-lenses, allow imaging within extended depths of turbid tissues, however their footprint causes profound mechanical damage to all overlying regions and their imaging performance is limited.

Progress in the domain of complex photonics enabled a new generation of minimally invasive, high-resolution endoscopes by substitution of the Fourier-based image relays with a holographic control of light propagating through apparently randomizing multimode optical waveguides. This form of endo-microscopy became recently a very attractive way to provide minimally invasive insight into hard-to-access locations within living objects.

Professor Čižmár will review our fundamental and technological progression in this domain and introduce several applications of this concept in bio-medically relevant environments.

AP 483 & AMO Seminar Series
Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

Computational imaging involves the joint design of imaging system hardware and software, optimizing across the entire pipeline from acquisition to reconstruction. Computers can replace bulky and expensive optics by solving computational inverse problems. This talk will describe new microscopes that use computational imaging to enable 3D fluorescence and phase imaging in samples that incur multiple scattering. Our reconstruction algorithms are based on large-scale nonlinear non-convex optimization. Applications span optical bioimaging, X-ray and electron microscopy.

AP 483 & AMO Seminar Series

Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

AP 483 & AMO Seminar Series
Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

CANCELLED - we apologize for any inconvenience.

Coherent detection provides large improvements in link margin that can enable new network architectures incorporating optical switching and routing. "Analog coherent" approaches based on optical phase locking can potentially eliminate the need for DSP, dramatically lowering power consumption and cost. This talk will provide background on the current role of optical interconnects in data centers and will highlight opportunities for photonics to dramatically improve the connectivity and performance of future installations. Integration of large-scale photonics with electronics in next generation multi-chip modules will be required, which raises a host of challenges and risks that provide fertile ground for research and innovation.

AP 483 & AMO Seminar Series
Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

AP 483 & AMO Seminar Series
Time:
4:15 pm, every Monday (Refreshments begin at 4 pm)

Location:
Spilker Building Room 232

Individuals of all genders invited to be a part of:
#StanfordToo: A Conversation about Sexual Harassment in Our Academic Spaces, where we will feature real stories of harassment at Stanford academic STEM in a conversation with Provost Drell, Dean Minor (SoM), and Dean Graham (SE3). We will have plenty of time for audience discussion on how we can take concrete action to dismantle this culture and actively work towards a more inclusive Stanford for everyone. While our emphasis is on STEM fields, we welcome and encourage participation from students, postdocs, staff, and faculty of all academic disciplines and backgrounds.

Rapid and precise measurements are and always have been of interest in science and technology partly because of their numerous practical applications. Since their development, frequency comb-based methods have revolutionized optical measurements. They simultaneously provide high resolution, high sensitivity, and rapid acquisition times. These methods are being developed for use in many fields, from atomic and molecular spectroscopy, to precision metrology, to spectral LIDAR and even atmospheric monitoring. However they cannot address the issues of inhomogeneously broadened transitions or sample heterogeneity. This is especially important for remote chemical sensing applications.

In this talk I will discuss a novel optical method, that I recently developed, which overcomes these limitations. I will demonstrate its capabilities for probing extremely weak fundamental processes as well as its applications for rapid and high resolution chemical sensing.

References:

B. Lomsadze, B. Smith and S. T. Cundiff. "Tri-comb spectroscopy". Nature Photonics 12, 676, 2018.
B. Lomsadze and S. T. Cundiff. "Frequency-comb based double-quantum two-dimensional spectrum identifies collective hyperfine resonances in atomic vapor induced by dipole-dipole interactions." Physical Review Letters 120, 233401, 2018.
B. Lomsadze and S. T. Cundiff. "Frequency combs enable rapid and high-resolution multidimensional coherent spectroscopy". Science 357, 1389, 2017
B. Lomsadze and S. T. Cundiff. "Frequency comb-based four-wave-mixing spectroscopy". Optics letters 42, 2346, 2017